Monopulse traffic sensor and method

ABSTRACT

A method and system for determining a position of a vehicle within a field of view using a traffic sensor are provided. This involves (a) mounting the traffic sensor at a fixed location relative to a road; (b) modulating a microwave signal to produce a periodic time-varying modulated signal; (c) radiating the periodic time-varying modulated microwave signal in a radiation beam at a vehicle on a road to generate a reflected modulated microwave signal, wherein the reflected periodic time-varying modulated microwave signal induces a first received signal at a first receiver antenna and a second received signal at a second receiver antenna, the second receiver being spaced from the first receiver; and, (d) determining the position of the vehicle on the road within the field of view based on the periodic time-varying modulated signal, the first received signal, and the second received signal, wherein the position of the vehicle is determinable during a single period of the periodic time-varying modulated signal. The position comprises a lateral position of the vehicle across a width of the road and a longitudinal position of the vehicle along a length of the road.

FIELD

This invention relates to a traffic sensor for traffic monitoring, andmore specifically to a monopulse radar system and method for use in atraffic sensor mounted at a fixed location with respect to a multilaneroad.

BACKGROUND

As urban centers increase in size, and traffic congestion becomes morecommon, the need for accurate and up-to-date traffic information alsoincreases. Traffic surveillance relies primarily on traffic sensors,such as inductive loop traffic sensors that are installed under thepavement, video sensors and radar sensors.

SUMMARY

In accordance with an aspect of an embodiment of the invention, there isprovided a method for determining a position of a vehicle within a fieldof view using a traffic sensor. The method comprises (a) mounting thetraffic sensor at a fixed location relative to a road; (b) modulating amicrowave signal to produce a periodic time-varying modulated signal;(c) radiating the periodic time-varying modulated microwave signal in aradiation beam at a vehicle on a road to generate a reflected modulatedmicrowave signal, wherein the reflected periodic time-varying modulatedmicrowave signal induces a first received signal at a first receiverantenna and a second received signal at a second receiver antenna, thesecond receiver being spaced from the first receiver; and, (d)determining the position of the vehicle on the road within the field ofview based on the periodic time-varying modulated signal, the firstreceived signal, and the second received signal, wherein the position ofthe vehicle is determinable during a single period of the periodictime-varying modulated signal. The position comprises a lateral positionof the vehicle across a width of the road and a longitudinal position ofthe vehicle along a length of the road.

In accordance with a further aspect of an embodiment of the invention,there is provided a traffic sensor for obtaining vehicular traffic datawithin a field of view. The sensor comprises 1) a transceiver unit forgenerating a frequency modulated microwave signal; 2) at least onetransmitter antenna for (i) receiving the modulated microwave signalfrom the transceiver unit, (ii) forming a radiation beam, and (iii)radiating a transmitted radiated signal, comprising the modulatedmicrowave signal in the radiation beam, at a vehicle; 3) a firstreceiver antenna for (i) receiving the modulated microwave signalreflected back from the vehicle, and (ii) generating a first receivedsignal; 4) a second receiver antenna for (i) receiving the modulatedmicrowave signal reflected back from the object, and (ii) generating asecond received signal, wherein the first receiver antenna is spacedfrom the second receiver antenna, and the transceiver unit is connectedto the first receiver antenna and to the second receiver antenna, toreceive the first received signal from the first receiver antenna andthe second received signal from the second receiver antenna; and, 5) aprocessor unit for determining a velocity and a position of a vehicle ona road, wherein the velocity is measured relative to the road andwherein the position comprises a lateral position of the vehicle acrossa width of the road and a longitudinal position of the vehicle along alength of the road. The processor unit is operable to determine thevelocity and the position of the vehicle on the road by (a) determiningthe two-dimensional position of the vehicle on the road based on thetime-varying modulated signal, the first received signal, and the secondreceived signal during a single period of the time-varying modulatedsignal; and, (b) repeating (a) at multiple times when the vehicle iswithin the field of view to determine a sequence of vehicle positions intwo dimensions and the velocity of the vehicle from the sequence ofvehicle positions in two dimensions.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of preferred embodiments is provided herein belowwith reference to the following drawings, in which;

FIG. 1, in a block diagram illustrates a monopulse traffic sensor inaccordance with an aspect of the present invention;

FIG. 2 is a schematic diagram of the sensor of FIG. 1 in the side fireconfiguration;

FIG. 3 is a schematic diagram of the sensor of FIG. 1 in the forwardlooking configuration;

FIG. 4 in a schematic view illustrates the sensor of FIG. 1 mounted inthe side fired configuration;

FIG. 5 is a flow chart diagram of the basic steps taken by the sensor ofFIG. 1; and,

FIG. 6 is a flow chart diagram of the steps taken by the processing unitof FIG. 1 when processing a received signal.

DETAILED DESCRIPTION

Referring to FIG. 1, illustrated therein is a monopulse traffic sensor10 made in accordance with an embodiment of the present invention.Monopulse traffic sensor 10 comprises a transmitting antenna 12 and tworeceiving antennas 14 and 16. Each of the antennas is in electricalcommunication with transceiver 18, which in turn is in electricalcommunication with processor unit 20 and stabilizer 22.

Processor unit 20 comprises modulator 24, analog to digital converter(ADC) 26 and digital signal processor (DSP) 28. Modulator 24 generates aprogrammable time-varying modulating signal that is received by thetransceiver unit 18. The transceiver unit 18 takes the programmabletime-varying modulating signal and generates a modulated microwavesignal that is received by the transmitting antenna 12. The antenna 12then forms a radiation beam and radiates the modulated microwave signalin the radiation beam 32 at an object or objects, such as a vehicle(shown in FIG. 4) or several vehicles. Reflected signal 33 is receivedby receiver antennas 14 and 16 as a result of reflections from theroadway and vehicles on the roadway of signal 32. Each receiver antennaproduces a received signal as a result of reflected signal 33. Thus,first receiver antenna 14 produces received signal 34 and secondreceiver antenna 16 produces received signal 36.

In various embodiments, sensor 10 may further comprise one or moretimers for determining an elapsed time. Each timer may be linked toprocessor unit 20 and may comprise any appropriate device for measuringtime. For example, the elapsed time could be measured by a clock signalinternal to processor unit 20 and therefore processor unit 20 maycomprise the timer. Alternatively, the timer could be a device separatefrom processor 20. The timer itself could determine the elapsed time orit could provide a signal to processor unit 20 from which processor unit20 can determine the elapsed time.

In some embodiments, sensor 10 may comprise a memory module that islinked to processor unit 20. The memory module may comprise anyappropriate device for storing data. For example, the memory module maycomprise a solid state memory device such as flash memory, SRAM, andDRAM. The above examples are not intended to be limiting in any manner.Furthermore, memory module may be part of or separate from processorunit 20.

The signal-stabilizing unit 22 receives a calibration portion of themodulated microwave signal produced by the transceiver. Thesignal-stabilizing unit 22 then derives a proportional calibrationsignal, which is measured by a processor-controlled circuit (not shown).The processor-controlled circuit then derives corrections based on thesemeasurements, which are used by the modulator 24 to correct theprogrammable time varying modulating signal. Optionally, DSP 28 may bethis processor that derives corrections based on the measurements of theproportional calibration signal. Alternatively, the processor thatderives corrections based on the measurements of the proportionalcalibration signal may be a separate processor, possibly part ofmodulator 24.

Each of the microwave signals received by receiver antenna 14 or 16, ispropagated to transceiver 18. At transceiver 18, first received signal34 and second received signal 36 are each mixed with the transmittersignal. The resulting signals are then low pass filtered. Thiseffectively down converts the received signals to produce intermediatefrequency (IF) signals. Specifically, first received signal 34 is downconverted to a first intermediate frequency signal and second receivedsignal 36 is down converted to a second intermediate frequency signal.Each of the intermediate frequency signals has a lower frequency thanthe received frequency signal from which it is produced; however, thefrequency shift, phase shift, and amplitude characteristics with respectto the transmitter signal are preserved. Specifically, the frequencyshift, phase shift, and amplitude characteristics of first receivedsignal 34 with respect to the transmitter signal are substantially thesame as the frequency shift, phase shift, and amplitude characteristicsof the first intermediate frequency signal with respect to thetransmitter signal. An analogous situation exists as between the secondreceived signal 36 and the second intermediate frequency signal.

Each intermediate frequency signal is amplified in the transceiver andthen forwarded to the ADC 26 of processor unit 20. ADC 26 converts eachsample of the first and second intermediate frequency signal, which areanalog signals, into a digital signal to provide first and seconddigitized signals respectively. Each of the first and second digitizedsignals is then propagated to DSP 28. DSP 28 processes the signals andextracts several parameters from the two signals such as the angle ofarrival and range of the target. The extracted parameters of the targetare then provided to microcomputer chip (MC) 29 for target tracking,analysis and reporting. Specifically, MC 29 comprises an internal,non-volatile memory (not shown) on which instructions for targettracking and analysis can be stored. MC 29 may also be operable tosubsequently configure this data for transmission to an external trafficmanagement system.

FIG. 2, in a schematic diagram, illustrates the sensor of FIG. 1 in theside fire configuration 40. In the side fire configuration, the signals32 and 33 are transmitted and reflected at an angle that is roughlyperpendicular to the path 42 of the target vehicles.

FIG. 3, in a schematic diagram, illustrates the sensor of FIG. 1 in theforward looking configuration 50. In the forward looking configuration,the signals 32 and 33 are transmitted and reflected at an angle that isroughly parallel to the path 52 of the target vehicles.

Various other embodiments utilize other configurations than the sidefire configuration or the forward-looking configuration. In particular,some embodiments may utilize a diagonal fire configuration. In thediagonal fire configuration the signals 32 and 33 are transmitted andreflected at an angle that is neither perpendicular nor parallel to thevelocities of vehicles on the road. In particular, in the diagonal fireconfiguration, signal 32 may be characterized by a first vector, whichis resolvable into a second and third vector. The second vector isroughly perpendicular to the direction of traffic. The third vector isroughly parallel to the direction of traffic. An analogous set ofvectors characterizes signal 33 as well.

Referring to FIG. 4, there is illustrated in a schematic view, themonopulse traffic sensor 10 mounted in the side fire configuration on apole 402 at the side of the roadway 404. Transmit antenna 12 (shown inFIG. 2) of sensor 10 transmits a signal 32 through a field of view 408at the road 404 to “paint” a long elliptical footprint on the road 404.Any non-background targets, such as vehicles 410, reflect signals suchas signal 33, which adds to the static background signal (clutter) andso is detectable and distinguishable by the sensor.

In the exemplary embodiment, the signal 32 transmitted by the transmitantenna 12 is a frequency modulated continuous wave (FMCW) signal. Themodulator sweeps through a range of frequencies. Specifically, thelow-power microwave signal 32 transmitted by sensor 10 has a constantlyvarying frequency, as controlled by the periodic modulating signal.Based on the frequency of the reflected signal 33 with respect to thetransmitter frequency, the sensor can determine when the original signalwas transmitted, thereby determining the time elapsed and the range tothe reflecting object.

Sensor 10 can be mounted at a height h on pole 402. In some embodimentsthe height is 5 meters. The side fired configuration is capable ofdetecting occluded vehicles. For example, in FIG. 4 vehicle 410 a isoccluded behind vehicle 410 b. However, a signal from sensor 10 is ableto reach vehicle 410 a along paths 414 and 416. A signal reflected offvehicle 410 a is able to reach sensor 10 by traversing the same path inreverse. This is possible because a signal traveling along path 414 isreflected by edge 411 in various directions including along path 416. Ananalogous affect is experienced by the signal that is reflected offvehicle 410 a in the direction of path 416. The reflected signalsreceived from vehicles 410 a and 410 b can be distinguished from oneanother through the range information and through the angle of arrivalinformation.

In various embodiments, regardless of whether the sidefire, forwardlooking, or diagonal fire configurations are used, receiver antennas 14and 16 are placed on one or more sides of the transmit antenna 12 andare spaced apart from each other by a distance d. The combined field ofviews of the receiver antennas 14 and 16 essentially overlap that of thetransmit antenna 12. In some embodiments, the antennas may be said tohave a squint angle of 0. The squint angle may be defined as the anglesubtended by the main axes of each receiver antenna with respect to eachother. When the squint angle is 0 the signals 34 and 36 will generallydiffer only in phase but not amplitude. The phase difference resultsfrom the fact that the antennas are not collocated but are ratherseparated by a distance d. This means that except for the special casewhere the target is directly in front of the radar, each of the receiverantennas 14 and 16 will be a slightly different distance from thetarget. This in turn means that the time it takes for the reflectedsignal to reach each of the receiver antennas will be slightlydifferent. As a result of this difference in timing, the signals 34 and36 received by each of the receiver antennas will be out of phase witheach other. In the case where the target is directly in front of theradar, the target will be equidistant from each of the receiver antennas14 and 16. In this case the reflected signal will reach each of thereceiver antennas 14 and 16 at the same time and therefore the receivedsignals 34 and 36 will be in phase. When there is no squint anglebetween the receiver antennas 14 and 16, the amplitudes of signals 34and 36 will not be appreciably different.

Alternatively, the receiver antennas 14 and 16 may be set up such thatthere is a squint angle between them: that is, their main axes are notparallel. In such a case, the received signals 34 and 36 will generallyvary in both amplitude and phase. The reason for the phase difference isthe same as that explained above. The reason for the difference inamplitude is that generally the reflected signal will intercept each ofthe receiver antennas at a different angle to its main axis. This willproduce a difference in the amplitude between the two received signals34 and 36 because the amplitude of the induced signal in an antennadepends on the angle between the antenna axis and the electric fieldinducing the signal.

The use of the two receiver antennas, allows for the measurement of theangle of arrival from even a single “pulse” or every modulation periodof the signal—hence the name monopulse. The angle of arrival is definedas the angle relative to the boresight of the transmit antenna at whichthe reflected signal arrives at sensor 10. The angle of arrival may bedetermined, within a certain margin of error, by subtracting one of thereceived signals from the other. In the exemplary embodiment the marginof error is approximately 5 degrees. The angle of arrival along with therange information may be used to determine the location of the targetvehicle in a two-dimensional plane.

More specifically, the difference in phase or amplitude between the twoinduced signals may be used to determine the angle of arrival. Asdescribed above, the phase of the signal received by either of receiverantennas 14 and 16 can be used to determine the distance from suchreceiver antenna to the target; however there is an ambiguity as to thetarget location. The difference in the phases of the signals received byeach of these antennas 14 and 16 can also be used to determine thedifference in the distance from each of the antennas 14 and 16 to thetarget thereby removing the ambiguity. Once this difference is known, itis a matter of trigonometry to determine the unambiguous position of thetarget relative to the sensor 10; in other words, it is a matter oftrigonometry to determine the angle of arrival of the target signal.

Thus, when phase monopulse is used, it is important to preserve thephase difference between the first and second received signals.Therefore, if the first and second received signals are processed insome manner, such as by either being down converted or digitized, thenit is preferable that they be processed in a manner that preserves thephase difference between them. This could for example, be done bysimultaneously processing the signals in equivalent circuits. This wouldensure that any delay introduced into one signal would be equal to thedelay in the other signal and therefore the phase difference wouldremain constant. However, given that the angle of arrival is derivedfrom the phase and not the amplitude, it is not necessary to preservethe amplitude difference between the two signals.

For example, as explained above, in the case of a phase difference, thedifference in phase determines the difference in length of the pathtraveled by the reflected signal to each antenna. In addition, asexplained above, the frequency of the reflected signal determines therange of the target relative to the transmit antenna. Thus, knowing thisdistance, the difference in the distance between the target and eachreceiver antenna, as well as the distance between the two antennas, onecan determine the position of the target relative to the sensor 10 in atwo dimensional plane.

With amplitude monopulse, the antennas 14 and 16 are oriented at asquint angle relative to one another such that a difference in amplituderesults. As mentioned above, the resulting signal amplitude in eachantenna is dependent on the angle at which the signal intercepts theantenna. Knowing the amplitude of the signal in each antenna, the anglebetween the two antennas, as well as the distance to the target one candetermine the position of the target relative to sensor 10 in a twodimensional plane.

Thus, when amplitude monopulse is used, it is important to preserve theamplitude difference between the first and second received signals.Therefore, if the first and second received signals are processed insome manner, such as by either being down converted or digitized, thenit is preferable that they be processed in a manner that preserves theamplitude difference between them. This could for example, be done byensuring that when the first and second received signals are processed,their amplitudes are affected in a substantially equivalent manner.Thus, if any gain or attenuation is introduced in one signal anequivalent gain or attenuation should be added to the other signal.However, given that the angle of arrival is derived from the amplitudeand not the phase, it is not necessary to preserve the phase differencebetween the two signals.

Thus, various embodiments of sensor 10, regardless of whether they usephase or amplitude information, are able to determine the position ofthe target relative to sensor 10 in a two dimensional plane. In otherwords, the position of a target vehicle could be determined as acombination of a lateral position across the width of the road and alongitudinal position along the length of the road. Since the positionof the target can be determined within a two-dimensional plane, sensor10 is able to determine the lane in which the vehicle is traveling.

In the side fire configurations, the use of range information maysuffice to estimate a lateral position across the length of the road.For example, it may be possible to estimate which lane the targetvehicle is traveling in based on the range information alone. However,the addition of the angle of arrival information allows for the accurateplacement of the vehicle in a longitudinal position along the length ofthe road, as well as a lateral position across the width of the road.

Similarly, in forward-looking configurations, the range information maybe sufficient to roughly estimate a longitudinal position of a targetvehicle along a length of the road. However, the addition of the angleof arrival information allows for the accurate placement of the vehiclein a lateral position across the width of the road, as well as alongitudinal position along the length of the road. For example, thiscould be used to determine which lane the vehicle is traveling in.

When sensor 10 is mounted in neither a side fire configuration nor aforward-looking configuration, it may not be possible to estimate eitherthe longitudinal or lateral position of the target vehicle from rangeinformation alone. In such a case, the use of both the range informationand the angle of arrival information may allow both the longitudinalposition and the lateral position of the vehicle on the road to bedetermined. Thus, as can be seen from the above discussion, regardlessof the configuration in which sensor 10 is mounted, the angle of arrivalinformation is helpful in determining at least one of the lateral andlongitudinal positions of the vehicle on the road.

Reference is now made to FIG. 5, which in a flow chart illustrates thesteps 500 taken by monopulse traffic sensor 10. At step 502, the signalis transmitted. At step 504, the reflected signal is received. At step506, the signal is processed and analyzed.

Reference is now made to FIG. 6, which in a flow chart illustrates thesteps 600 taken by the processing unit 20 in processing and analyzingthe received signals. This diagram corresponds to step 506 of FIG. 5. Atstep 602, ADC 26 captures time domain samples from the two receiverantennas and provides the digitized signal to DSP 28. At step 604, thetime domain samples are converted to range domain vectors. This steppreserves the amplitudes and phases of each of the received signalsrelative to the time domain vector. This step is accomplished byperforming a weighted complex Fast Fourier Transformation (FFT) processon the two signals.

At step 606, a complex sum and difference is performed on the two rangedomain vectors derived from the two received signals from thecorresponding two receivers, thereby yielding sum and differencevectors, Σ_(i) and Δ₁, where i designates range bin number.

At step 608, the sum vector Σ_(i) is used as a preliminary targetdetection vector R_(i). This is accomplished by ignoring the phase andsumming the amplitude of the two signals. This yields a better signal tonoise ratio and provides a better signal for detecting target vehiclesby combating phase interference that may cause nulls.

Nulls occur when a vehicle, which is moving through the field of view ofa sensor, is at such a position with respect to the sensor that thecomplex radar-cross section of the vehicle causes the amplitude of thereceived signal at a receiver antenna of the sensor to fall to a lowlevel. In some cases, this could lead the sensor to erroneously concludethat the vehicle is no longer within its field of view. This in turn cancause the sensor to drop the presence detection of the target vehicleand consequently ignore the vehicle. In addition, when the vehicleleaves the position at which the null occurred and the amplitude of thereceived signal rises to a higher level, the sensor may erroneouslyconclude that a new vehicle has entered its field of view. Thus, if thesensor were used to count the number of vehicles moving through itsfield of view on the road, then this could lead to an erroneous count.However, the use of two antennas in various embodiments of trafficsensor 10 can reduce the effect of nulls and improve overall sensorperformance.

In various embodiments of traffic sensor 10, the level of the receivedsignal in each range i is used to detect the presence and range of thetarget. Detection is based upon the signal exceeding the backgroundlevel. Due to limitations in the sensor's resolution, typically areceived signal will “spill” its energy into several range bins. In sucha case, the target vehicle's range can be determined to be the point atwhich a local peak of the amplitude of the received signal occurs.

An important limiting factor on a sensor's accuracy is its ability todetect targets that are occluded by other targets (such as vehicle 410 adepicted in FIG. 4). Although signal diffraction allows for thereception of reflected signals from the occluded target, in many casesthese signals will be lower in amplitude than those of the clearlyvisible target. In such a case, the occluded target's signal may not bethe peak signal and may therefore be ignored. However, in variousembodiments of traffic sensor 10, the addition of another parameter,namely the angle of arrival, allows the processor to improve itsresolution of distinct targets in such cases, leading to improvedperformance.

At step 610, the difference vector Δ_(i) is normalized by dividing it bythe sum vector Σ_(i). This produces a vector that yields an amplitudeinvariant angle of arrival. The normalization process corrects for anyerrors, which may occur as a result of weak signals. Even within nullsor low signal levels, the phases of the signals are preserved, allowingangle processing. Therefore, the normalization provides for anunambiguous function for converting the differences in the signals intoangle of arrival information.

At step 612, various corrections are performed on the normalized vector(Δ_(i)/Σ_(i)) produced at step 610. Some examples of the correctionsthat could be performed include: linearization of the arcSin function,corrections against very weak signals and ‘guard’ functions againstMultipathing. This step yields a linear angle of arrival vector α_(i).

At step 614, the target detection vector R_(i) and linear angle ofarrival vector at are used to obtain a 2D position vector of each targetvehicle. In addition, the position of each vehicle is tracked todetermine the vehicle's velocity vector. More specifically, the positionis determined multiple times while the vehicle is in the field of viewto provide a sequence of positions in two dimensions defined by aposition vector. The velocity can then be calculated from the rate ofchange of the position vector within a given time frame.

At step 616, the information produced in the previous steps isintegrated in order to provide additional information. For example,integrating the information makes it possible to resolve vehicles thatmay otherwise have been ignored. For example, the vectors can beintegrated over distance, which would reveal a curve of signal strengthat specific distances. This information could reveal all objects in thefield of view of sensor 10, including vehicles occluded by othervehicles. As discussed above, reflections from occluded vehicles producevery weak received signal strengths. Normally these weak signals mightbe ignored as noise. However, integration of the vectors would reveal acontinuous pattern of the weak signal at a given distance, whichrepresents a reflecting object. In contrast, noise would result in arandom pattern. Therefore, a vehicle that might normally be ignoredwould be more likely to be detected.

This same process reveals the length of each vehicle in that theintegration of the vectors would reveal where each reflection begins andwhere it ends. This information allows for the calculation of the lengthof each vehicle detected by the sensor 10. Alternatively, the length canalso be determined from dwell time and velocity of the vehicle. Morespecifically, the dwell time can be measured as the total amount of timethat the vehicle is present within field of view of sensor 10. The dwelltime may be measured by the timer mentioned above. Then the velocityalong with the dwell time can used to determine the length of thevehicle. Following that the vehicle can be classified according to itslength.

The various classes may be stored in the above-mentioned memory module.The number of classes and types of classes may vary between embodiments.For example, some embodiments may use categories such as trucks,midsized cars, small cars and motorcycles. Other embodiments may usedifferent categories and may use a different number of categories.

At step 618, the information is further integrated to producestatistical information such as the volume of traffic on the roadway,the occupancy, the average speed of vehicles, and the vehicle lengthclass distribution by lane of roadway.

In various embodiments traffic sensor 10 is capable of determiningstatistical vehicle data. For example, in some embodiments, trafficsensor 10 is capable of determining the number of vehicles traveling inthe direction of traffic. More specifically, in some embodiments this isachieved by processor 20 incrementing a counter for each vehicledetected traveling in the direction of traffic.

In various other embodiments, sensor 10 can determine the averagevelocity of vehicles traveling in the direction of traffic in onedirection along the road, by processor 20 first summing the velocity ofeach vehicle detected traveling in the direction of traffic on the roadand then dividing the result by the number of vehicles detectedtraveling in the direction of traffic.

Furthermore, in some embodiments, sensor 10 can determine the number ofvehicles traveling in a lane, by processor 20 incrementing a counter foreach vehicle detected traveling in the lane.

In some embodiments, sensor 10 can calculate the average velocity ofvehicles in a lane, by processor 20 summing the velocity of each vehicledetected traveling in the lane and then dividing this sum by the numberof vehicles detected traveling in the lane.

Moreover, in certain embodiments, sensor 10 can determine the occupancyof a lane of the roadway, by processor 20 determining a sum ofdwell-time of all vehicles detected traveling in the lane during theelapsed time, and then dividing the sum of dwell-time of all vehiclesdetected traveling in the lane by the elapsed time. The elapsed time maybe determined by use of the timer described above.

Further still, in some embodiments, sensor 10 can determine the numberof vehicles in a class of vehicles traveling on the road. Processor 20can determine this by incrementing a counter for each vehicle detectedin the class. For example, processor 20 may classify vehicles over apredetermined length as trucks. Then, by applying the above-describedmethod, processor 20 can determine the number of trucks traveling on thehighway. Moreover, processor 20 may perform these steps in relation to anumber of different classes of vehicles. This information can then beused to determine the breakdown of vehicular traffic on the road byclass of vehicle.

Similarly, in some embodiments, processor 20 can determine the number ofvehicles in a class of vehicles traveling in a lane of the road, byincrementing a counter for each vehicle in a class of vehicles detectedtraveling in the lane of the road. Thus, processor 20 may use thismethod to determine the number of trucks traveling in a specific lane ofthe road such as the left most lane. Similarly, processor 20 may usethis method to determine the number of midsized cars traveling in eachlane of the road. In various embodiments, processor 20 may perform thesesteps in relation to a number of different lanes and classes ofvehicles. This information may then be used to determine the breakdownof vehicular traffic by class of vehicle in each lane of traffic.

Furthermore, in various embodiments, processor 20 may determine theaverage velocity of vehicles in a class of vehicles. Processor 20 mayaccomplish this by summing the velocities of all vehicles detected in aclass of vehicles and dividing by the total number of vehicles detectedin the class. For example, this could be used to determine, the averagevelocity of midsized cars traveling on the road. More generally, invarious embodiments, this information can be used to determine theaverage velocity for each class of vehicles traveling on the road.

Similarly processor 20 may determine the average velocity of vehicles ina class of vehicles traveling in a lane by first summing the velocitiesof all vehicles in the class of vehicles traveling in the lane and thendividing by the total number of vehicles in the class of vehiclesdetected in the lane. This could for example be used to determine theaverage speed of trucks in a particular lane of the road. In variousembodiments, processor 20 may perform these steps in relation to anumber of different classes of vehicles and lanes of the road. Thus,this information may be utilized in order to determine the averagevelocity of each class of vehicle traveling in each lane of the road.

In some embodiments, sensor 10 may transmit signals to an externaltraffic management system. These signals may be transmitted through, forexample, a network. In various embodiments, sensor 10 is capable oftransmitting traffic data to an external traffic management system.These signals may be further processed by the external trafficmanagement system. In some embodiments, some or all of theabove-described determination of traffic data statistics may occur atthe external traffic management system. For example, the average speedof vehicles in a class of vehicles or the average speed of vehicles in agiven lane may be determined at the external traffic management system.

Other variations and modifications of the invention are possible. Allsuch modifications or variations are believed to be within the sphereand scope of the invention as defined by the claims appended hereto.

1. A method for determining a position of a vehicle within a field ofview using a traffic sensor, the method comprising: a) mounting thetraffic sensor at a fixed location relative to a road; b) modulating amicrowave signal to produce a periodic time-varying modulated signal; c)radiating the periodic time-varying modulated microwave signal in aradiation beam at a vehicle on a road to generate a reflected modulatedmicrowave signal, wherein the reflected periodic time-varying modulatedmicrowave signal induces a first received signal at a first receiverantenna and a second received signal at a second receiver antenna, thesecond receiver being spaced from the first receiver; and, d)determining the position of the vehicle on the road, wherein theposition comprises a lateral position of the vehicle across a width ofthe road and a longitudinal position of the vehicle along a length ofthe road, within the field of view based on the periodic time-varyingmodulated signal, the first received signal, and the second receivedsignal, wherein the position of the vehicle is determinable during asingle period of the periodic time-varying modulated signal.
 2. Themethod as defined in claim 1 wherein step d) comprises determining adifference between the first received signal and the second receivedsignal to determine at least one of the lateral position andlongitudinal position of the vehicle within the field of view.
 3. Themethod as defined in claim 2 wherein step d) comprises, determining anangle of arrival of the reflected periodic time-varying modulatedmicrowave signal based on the periodic time-varying modulated signal,and the difference between the first received signal and the secondreceived signal; determining the range of the vehicle by comparing oneof the received signals to the radiated signal; and, determining thelateral position and the longitudinal position of the vehicle from therange and angle of arrival.
 4. The method as defined in claim 3 whereinstep c) comprises radiating the periodic time-varying modulatedmicrowave signal in the radiation beam at the vehicle on the road from aside fire position at a side of the road, wherein the radiation beam issubstantially perpendicular to a direction of traffic on the road. 5.The method as defined in claim 4 further comprising repeating step d) atmultiple times when the vehicle is within the field of view to determinea sequence of positions in two dimensions and the velocity of thevehicle from the sequence of vehicle positions in two dimensions.
 6. Themethod as defined in claim 5 further comprising determining a dwell timeof the vehicle within the field of view; and, a length of the vehiclebased on the dwell time and the velocity of the vehicle.
 7. The methodas defined in claim 6 further comprising providing a plurality ofvehicle classifications; and, assigning a classification within theplurality of vehicle classifications to the vehicle based on the lengthof the vehicle.
 8. The method as defined in claim 3 wherein step c)comprises radiating the periodic time-varying modulated microwave signalin the radiation beam at the vehicle on the road from a forward fireposition over the road, wherein the radiation beam is substantiallyparallel to a direction of traffic on the road.
 9. The method as definedin claim 8 wherein step (d) comprises determining a lane occupied by thevehicle based on the lateral position of the vehicle.
 10. The method asdefined in claim 3 wherein a frequency of the periodic time-varyingmodulated signal varies at a known rate of change of frequency; thedifference is a difference in phase between the first received signaland the second received signal; and, at least one of the longitudinalposition and the lateral position of the vehicle within the field ofview is determined based on the known rate of change of frequency andthe difference in phase between the first received signal and the secondreceived signal.
 11. The method as defined in claim 3 wherein the firstreceiver antenna is oriented to be parallel to a first axis; the secondreceiver antenna is oriented to be at a non-zero angle to the firstaxis; the difference is a difference in amplitude between the firstreceived signal and the second received signal; and, the angle ofarrival of the vehicle within the field of view is determined based onthe difference in amplitude between the first signal and the secondsignal.
 12. The method as defined in claim 1 wherein step c) comprisesradiating the modulated microwave signal in the radiation beam at thevehicle on the road from a diagonal fire position with respect to theroad, wherein i) the radiation beam is characterized by a first vector,ii) the first vector is resolvable into a second vector and a thirdvector, iii) the third vector is orthogonal to the second vector, iv)the second vector is substantially parallel to a direction of traffic onthe road, and v) the third vector is substantially perpendicular to thedirection of traffic on the road.
 13. The method as defined in claim 1further comprising: down converting the first received signal to producea first intermediate frequency signal, wherein the frequency of thefirst intermediate frequency signal is less than the frequency of thefirst received signal; and, down converting the second received signalto produce a second intermediate frequency signal, wherein the frequencyof the second intermediate frequency signal is less than the frequencyof the second received signal; wherein a difference in a selectedcharacteristic between the first intermediate frequency signal and thesecond intermediate frequency signal substantially corresponds to adifference in the selected characteristic between the first receivedsignal and the second received signal, wherein the selectedcharacteristic is at least one of phase and amplitude; wherein step d)comprises determining the position of the vehicle on the road based onthe first intermediate frequency signal, the second intermediatefrequency signal and a modulated intermediate frequency signalcorresponding to, and having a lower frequency than, the modulatedsignal.
 14. The method as defined in claim 13 further comprising:digitizing the first intermediate frequency signal to produce a firstdigitized signal; and, digitizing the second intermediate frequencysignal to produce a second digitized signal; wherein a difference in theselected characteristic between the first digitized signal and thesecond digitized signal substantially corresponds to a difference in theselected characteristic between the first intermediate frequency signaland the second intermediate signal; wherein step d) comprisesdetermining a position of the vehicle on the road based on the firstdigitized signal, the second digitized signal, and a digital modulatedsignal corresponding to the modulated intermediate frequency signal. 15.The method as defined in claim 14 wherein step d) further comprises:determining a sum of the first digitized signal and the second digitizedsignal; determining a difference between the first digitized signal andthe second digitized signal; dividing the difference by the sum toproduce a normalized difference; and, determining the angle of arrivalfrom the normalized difference.
 16. The method as defined in claim 1further comprising: incrementing a vehicle count for each vehicledetected traveling in a direction of traffic.
 17. The method as definedin claim 16 further comprising: for each vehicle detected traveling inthe direction of traffic: determining a velocity of each vehicle;determining a velocity sum by summing the velocity of each vehicle; and,determining an average velocity of vehicles traveling in the directionof traffic by dividing the velocity sum by the vehicle count.
 18. Themethod as defined in claim 1 further comprising: selecting a selectedlane; and, incrementing a selected-lane vehicle count for each vehicledetected in the selected lane.
 19. The method as defined in claim 18further comprising: for each vehicle detected in the selected lane:determining a velocity of each vehicle; determining a selected-lanevelocity sum by summing the velocity of each vehicle; and, determiningan average velocity of vehicles in the selected lane by dividing theselected-lane velocity sum by the selected-lane vehicle count.
 20. Themethod as defined in claim 18 further comprising: determining a dwelltime of each vehicle within the selected lane during an elapsed time;and, determining a lane occupancy by i) determining a sum of the lanevehicle dwell-times during the elapsed time and then ii) dividing theselected-lane vehicle dwell-time sum by the elapsed time.
 21. The methodas defined in claim 1 further comprising: repeating step d) at multipletimes when the vehicle is within the field of view to determine avelocity of the vehicle; determining a dwell time of the vehicle withinthe field of view; determining a length of the vehicle based on thedwell time and the velocity of the vehicle; providing a plurality ofvehicle classifications wherein the classification is based on thelength of a vehicle; and, for each class of vehicles in the plurality ofvehicle classifications, incrementing a class vehicle count for eachvehicle detected in that class of vehicles.
 22. The method as defined inclaim 21 further comprising, for a least one class of vehicles,determining a class velocity sum by summing the velocity of each vehiclein the class of vehicles; and, determining an average velocity ofvehicles in the class of vehicles by dividing the class velocity sum bythe class vehicle count.
 23. The method as defined in claim 1 furthercomprising: selecting a selected lane; providing a plurality of vehicleclassifications wherein the classification is based on the length of avehicle; selecting a selected class of vehicles from the plurality ofvehicle classifications; and, incrementing a lane-class vehicle countfor each vehicle in the selected class detected in the selected lane.24. The method as defined in claim 23 further comprising: determiningthe velocity of each vehicle in the selected class of vehicles in theselected lane; determining a lane-class velocity sum by summing thevelocity of each vehicle in the selected class of vehicles in theselected lane; and, determining an average velocity of the vehicles inthe selected class of vehicles in the selected lane by dividing thelane-class velocity sum by the lane class velocity count.
 25. The methodof claim 5 further comprising the steps of: coupling the traffic sensorto an external traffic management system; and, transmitting a signalfrom the traffic sensor to the external traffic management systemwherein the signal is representative of at least one of the position andthe velocity of the vehicle.
 26. A traffic sensor for obtainingvehicular traffic data within a field of view, the sensor comprising: atransceiver unit for generating a frequency modulated microwave signal;at least one transmitter antenna for (i) receiving the modulatedmicrowave signal from the transceiver unit, (ii) forming a radiationbeam, and (iii) radiating a transmitted radiated signal, comprising themodulated microwave signal in the radiation beam, at a vehicle; a firstreceiver antenna for (i) receiving the modulated microwave signalreflected back from the vehicle, and (ii) generating a first receivedsignal; and, a second receiver antenna for (i) receiving the modulatedmicrowave signal reflected back from the object, and (ii) generating asecond received signal, wherein the first receiver antenna is spacedfrom the second receiver antenna, and the transceiver unit is connectedto the first receiver antenna and to the second receiver antenna, toreceive the first received signal from the first receiver antenna andthe second received signal from the second receiver antenna; a processorunit for determining a velocity and a position of a vehicle on a road,wherein the velocity is measured relative to the road and wherein theposition comprises a lateral position of the vehicle across a width ofthe road and a longitudinal position of the vehicle along a length ofthe road, by (a) determining the two-dimensional position of the vehicleon the road based on the time-varying modulated signal, the firstreceived signal, and the second received signal during a single periodof the time-varying modulated signal; and, (b) repeating (a) at multipletimes when the vehicle is within the field of view to determine asequence of vehicle positions in two dimensions and the velocity of thevehicle from the sequence of vehicle positions in two dimensions. 27.The traffic sensor as defined in claim 26 further comprising a timer fordetermining a dwell time of the vehicle within the field of view;wherein the processor is further operable to determine a length of thevehicle based on the dwell time and the velocity of the vehicle.
 28. Thetraffic sensor as defined in claim 27 further comprising a memory forstoring a plurality of vehicle classifications, wherein the processor islinked to the memory and is further operable to assign a classificationwithin the plurality of vehicle classifications to the vehicle based onthe length of the vehicle.
 29. The traffic sensor as defined in claim 26wherein step a) comprises determining a difference between the firstreceived signal and the second received signal to determine at least oneof the lateral position and the longitudinal position of the vehiclewithin the field of view.
 30. The traffic sensor as defined in claim 26wherein step a) comprises determining an angle of arrival of thereflected modulated microwave signal based on the time-varying modulatedsignal, and the difference between the first received signal and thesecond received signal; determining the range of the vehicle bycomparing one of the received signals to the transmitted radiatedsignal; and, determining the lateral position and the longitudinalposition of the vehicle from the range and angle of arrival.
 31. Thetraffic sensor as defined in claim 30 wherein a frequency of thetime-varying modulated signal varies at a known rate; the difference isa difference in phase between the first received signal and the secondreceived signal; and, the processor is operable to determine at leastone of the longitudinal position and the lateral position of the vehiclewithin the field of view based on the known rate and the difference inphase.
 32. The traffic sensor as defined in claim 30 wherein the firstreceiver antenna is oriented to be parallel to a first axis; the secondreceiver antenna is oriented to be at a non-zero angle to the firstaxis; the difference is a difference in amplitude between the firstreceived signal and the second received signal; and, the processor isoperable to determine the angle of arrival of the vehicle within thefield of view based on the difference in amplitude between the firstreceived signal and the second received signal.
 33. The traffic sensoras defined in claim 26 wherein the processor is further operable todetermine the number of vehicles traveling in a direction of traffic byincrementing a vehicle count for each vehicle detected traveling in thedirection of traffic.
 34. The traffic sensor as defined in claim 33wherein the processor is further operable to determine an averagevelocity of vehicles traveling in the direction of traffic bydetermining a velocity sum by summing the velocity of each vehicle; and,dividing the velocity sum by the vehicle count.
 35. The traffic sensoras defined in claim 26 wherein the processor is further operable todetermine the number of vehicles traveling in a lane by incrementing alane vehicle count for each vehicle detected in the lane.
 36. Thetraffic sensor as defined in claim 35 wherein the processor is furtheroperable to determine an average velocity of vehicles traveling in thelane by determining a lane velocity sum by summing the velocity of eachvehicle detected traveling in the lane; and, dividing the lane velocitysum by the lane vehicle count.
 37. The traffic sensor as defined inclaim 26 further comprising a timer for determining a lane vehicle dwelltime of each vehicle traveling in the lane within the field of viewduring an elapsed time; wherein the processor is further operable todetermine a lane occupancy during the elapsed time by i) determining asum of the lane vehicle dwell-times during the elapsed time and then ii)dividing the sum of the lane vehicle dwell-times by the elapsed time.38. The traffic sensor as defined in claim 28 wherein the processor isfurther operable to determine the number of vehicles detected in a classof vehicles by, for each class of vehicles in the plurality of vehicleclassifications, incrementing a class vehicle count for each vehicledetected in that class of vehicles.
 39. The traffic sensor as defined inclaim 38 wherein the processor is further operable to determine anaverage velocity of vehicles in a class of vehicles by determining aclass velocity sum by summing the velocity of each vehicle in the classof vehicles; and, dividing the class velocity sum by the class vehiclecount.
 40. The traffic sensor as defined in claim 28 wherein theprocessor is further operable to, for at least one class of vehicles,determine the number of vehicles in the class of vehicles detected in alane of the road by incrementing a lane-class vehicle count for eachvehicle in the class of vehicles detected in the lane.
 41. The trafficsensor as defined in claim 40 wherein the processor is further operableto determine, for at least one class of vehicles, an average velocity ofvehicles in the class of vehicles detected in the lane by determining alane-class velocity sum by summing the velocity of each vehicle in theclass of vehicles detected in the lane; and, dividing the lane-classvelocity sum by the lane-class vehicle count.